bigdata

问题 I have come across several sources of information, such as the one found here, which explain "predicate pushdown" as : … if you can “push down” parts of the query to where the data is stored, and thus filter out most of the data, then you can greatly reduce network traffic. However, I have also seen the term "projection pushdown" in other documentation such as here, which appears to be the same thing but I am not sure in my understanding. Is there a specific difference between the two terms?

问题 I have the following workflow, whereby I append data to an empty pandas Series object. (This empty array could also be a NumPy array, or even a basic list.) in_memory_array = pd.Series([]) for df in list_of_pandas_dataframes: new = df.apply(lambda row: compute_something(row), axis=1) ## new is a pandas.Series in_memory_array = in_memory_array.append(new) My problem is that the resulting array in_memory_array becomes too large for RAM. I don't need to keep all objects in memory for this

问题 I was learning hadoop, I found number of reducers very confusing : 1) Number of reducers is same as number of partitions. 2) Number of reducers is 0.95 or 1.75 multiplied by (no. of nodes) * (no. of maximum containers per node). 3) Number of reducers is set by mapred.reduce.tasks . 4) Number of reducers is closest to: A multiple of the block size * A task time between 5 and 15 minutes * Creates the fewest files possible. I am very confused, Do we explicitly set number of reducers or it is

问题 Disclaimer : Many of you pointed to a duplicated post, I was aware of it but I believe it's not a fair duplicate as some way of saving/loading might be different for data frames and lists. For instance the packages fst and feather work on data frames but not on lists. My question is specific to lists . I have a ~50M element list and I'd like to save it to a file to share it among different R sessions. I know the native ways of saving in R ( save , save.image , saveRDS ). My point was : would

问题 Disclaimer : Many of you pointed to a duplicated post, I was aware of it but I believe it's not a fair duplicate as some way of saving/loading might be different for data frames and lists. For instance the packages fst and feather work on data frames but not on lists. My question is specific to lists . I have a ~50M element list and I'd like to save it to a file to share it among different R sessions. I know the native ways of saving in R ( save , save.image , saveRDS ). My point was : would

来源： https://stackoverflow.com/questions/64490738/6-gb-ram-fails-in-vectorizing-text-using-word2vec

来源： https://stackoverflow.com/questions/64490738/6-gb-ram-fails-in-vectorizing-text-using-word2vec

来源： https://stackoverflow.com/questions/64490738/6-gb-ram-fails-in-vectorizing-text-using-word2vec

来源： https://stackoverflow.com/questions/64490738/6-gb-ram-fails-in-vectorizing-text-using-word2vec

来源： https://stackoverflow.com/questions/52091433/hive-alter-table-change-column-name-gives-null-to-the-renamed-column